A conventional exhaust cabinet includes a cabinet. On the upper end of the cabinet is provided with a shelter plate with an opening. In the rear of the cabinet, a flow-guide plate is vertically disposed and the flow-guide plate is provided with a specially designed opening. Through the opening of the shelter plate and the opening of the flow-guide plate in the rear of the cabinet, harmful gas can be drawn out by using an air-extraction machine and ducts. When the exhaust cabinet is used, the air-extraction machine should be operated correspondingly in order to continue air extraction. During this moment, the door of the cabinet should not be closed completely or an opening should be provided at the doorsill in advance in order to prevent from free-running and consequent burning of a motor resulting from failing to supplying air. Besides, when in use, it is usually necessary to open the door of the cabinet to an approximate height to facilitate operators stretching their hands into the cabinet for experimental operations. However, when the door of the conventional exhaust cabinet is open, based on the principles of Aerodynamics, harmful gas within the cabinet may escape easily around the peripheries of the door. Moreover, the leakage may be even severer when operators are opening or closing the door or stand in front of the open cabinet for experimental operations, or when there are ambient drafts or there are people walking by. The main reason of the leakage is that vortex and turbulence are easily formed around the peripheries of the cabinet door and around operators' chests. The vortex and turbulence may result in the mass and momentum exchange between the inside and the outside of the cabinet. Therefore, the leakage of the pollutants in the cabinet is hardly avoidable. Unfortunately, there is nearly no conventional exhaust cabinet can be used without opening and closing its door. In other words, operators can operate their experiments only when the cabinet is open. Besides, the exhaust cabinet is scarcely placed in the environment where there is no ambient air turbulence or there are no people walking by. As a result, in the laboratories, factories, or buildings using the conventional exhaust cabinets, people usually smell the sour odor emitted from chemicals because pollutants continue leaking from the cabinets. Operators and people working thereby may get used to the odor and long-term chemical pollution occurs.
In order to solve the leakage problem resulting from using above conventional exhaust cabinet, a push-pull type exhaust cabinet was developed by US patent (U.S. Pat. No. 7,318,771). As shown in FIGS. 8 and 9, the push-pull type exhaust cabinet “a” mainly includes a cabinet “b”. A space is formed in front of the cabinet “b” while an air-extraction slot “c” is formed at the lower part of the front end of the cabinet “b”. Besides, a screen board “d” is provided at the upper part of the cabinet “b” for natural air supply. The upper part “e1” of a bi-layered hollow cabinet door “e” is fixed to two sides of the front end of the cabinet “b” while the lower part “e2” thereof is designed to be telescopic, that is, is able to move upward or downward relative to the upper part “e1”. When the lower part “e2” is pulled upward, the front end of the cabinet “b” can be closed. Moreover, an air blow slot “e3” is formed in the lower part “e2”. When a transverse fan “f” is provided to blow air downward through the air blow slot “e3” while an air-extraction device “g” is provided to draw in the air through the air-extraction slot “c”, an air curtain “h” can be formed between the air blow slot “e3” and the air-extraction slot “c” that are disposed correspondingly to each other in order to remove harmful gas.
The left, right, and rear sides of the cabinet of the push-pull type exhaust cabinet are completely closed to prevent from the leakage of harmful gas while the front side thereof is provided with an open space for operation. However, in practice, because the air curtain forms at the interface of the cabinet door's opening, ambient air turbulence evoked by operators' operation or other factors in the outer environment may result in the leakage of pollutant gas. For example, when the position at which the pollutant source is released is too high or the hands of an operator are fairly close to the air blow source of the bi-layered cabinet door, it may evoke some problems, such as a problem that the internal space of the cabinet is insufficient, another problem that the air extraction ability should be greatly elevated, or still another problem that the pollutants may leak through the hands of the operator. Moreover, under the condition of producing high-temperature harmful gas or of emergency, it is necessary to decrease the extent of the opening of the cabinet door of the push-pull type exhaust cabinet and increase the amount of air extraction. These are all the shortcomings required to overcome.
In order to overcome above shortcomings, inventor had the motive to study and develop the present invention. After hard research and development, the inventor provides a reverse oblique air curtain exhaust cabinet, by using which it is able to reduce effectively the leakage of pollutants, to enhance the ability against the ambient air turbulence, and to remove pollutants in a more energy-saving way.